Evaluating the Applicability of Large-Diameter Cement Deep Mixing Method for Soft Ground Improvement: A Landmark Case Study in Vietnam

The conventional cement deep mixing (CDM) method, which employs a single mixing shaft with unidirectional rotation, often produces small-diameter columns, leading to limitations in productivity and column quality, especially in large-scale ground improvement projects. This paper presents advantages of a large-diameter CDM technique, commercially known as the Reliable Accord Soil (RAS) method, over the traditional CDM approach. Extensive experimental investigations were conducted during trial and mass construction phases at Lach Huyen Port, Vietnam. During the trial phase, the influence of operational parameters, including number of blade cuts, penetration speed, and flow rate of grout on the unconfined compressive strength (UCS) of column cores were examined. In the mass construction phase, the UCS, Rock Quality Designation (RQD), and equivalent elastic modulus (Es) values of core samples from RAS and CDM columns were analysed and compared alongside their respective productivity. Results from the trial phase demonstrated clear correlations that the UCS value of core samples increased with the increase in the number of blade cuts and flow rate whereas it decreased with the increase in the penetration speed. In the mass construction phase, the RAS method resulted in significantly higher average RQD, UCS, and Es values (88.9%, 2.23 MPa, 562.53 MPa, respectively) compared to that from the CDM method (86.86%, 1.89 MPa, 475.95 MPa, respectively) although the cement content used for the RAS method was just 80% of that for CDM method. Furthermore, under similar geological conditions and operational parameters, the RAS method achieved a productivity (45.54 m3/h) of 2.9 times higher than that of CDM method (15.35 m3/h). These findings highlight the superior performance and efficiency of the RAS method, offering valuable insights for its application in large-scale ground improvement projects.